Bump actions/checkout from 5 to 6 (#67)

Author: 153957

.github/workflows/build.yml

@@ -7,7 +7,7 @@ jobs:
   notebooks:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v5
         with:
           python-version: '3.10'
@@ -24,7 +24,7 @@ jobs:
   index:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v5
         with:
           python-version: '3.10'
@@ -41,7 +41,7 @@ jobs:
   pdf:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: xu-cheng/latex-action@v2
         with:
           root_file: "*/*.tex"